1. Field of the Invention
The present invention relates to a vibration wave (vibration type) motor driving device for driving a vibration wave (vibration type) motor.
2. Related Background Art
As a determination method used when a motor cannot be driven due to an overload or the like during controlling a target object, a method of determining that driving is impossible when the driving portion of the motor is not driven for a predetermined time or more is used frequently. For example, in voltage-controlled DC motors and the like, this determination is performed with application of a maximum voltage. However, in frequency-controlled vibration wave motors which have been put into practical applications, proper driving impossibility determination cannot be attained. The reason is as follows. A frequency-controlled vibration wave motor generates a maximum torque during rotation at frequencies near the resonance frequency as its characteristics, but the resonance frequency changes depending on environmental conditions such as temperatures. If a driving impossibility determination frequency is greatly shifted from the resonance frequency, the motor may not be driven regardless of a load.
To solve this problem, a method has been proposed in which a driving impossibility determination time is prolonged, and a range of driving frequency is swept during this driving impossibility determination time.
In the above-mentioned method, however, the driving impossibility determination time is set constant regardless of the magnitudes of frequencies with respect to the resonance frequency. With this setting, a motor is kept energized at frequencies near the resonance frequency for an excessively long time until it is determined that driving is impossible, resulting in an increase in power consumption.